Use of Salmonella vectors for vaccination against helicobacter infection

Abstract

The invention provides a method of immunization against helicobacter, involving mucosal administration of an attenuated salmonella vector including a nucleic acid molecule encoding a helicobacter antigen, and parenteral administration of a soluble helicobacter antigen, co-administered with a suitable parenteral adjuvant. Also provided by the invention are attenuated salmonella vectors for use in this method.

Description

This application is a continuation-in-part of PCT/US98/08890, which s filed on Apr. 30, 1998.

BACKGROUND OF THE INVENTION

This invention relates to the use of Salmonella vectors in vaccination methods against Helicobacter infection.

Helicobacter is a genus of spiral, gram-negative bacteria that colonize the gastrointestinal tracts of mammals. Several species colonize the stomach, most notably H. pylori, H. heilmanii, H. felis, and H. mustelae. Although H. pylori is the species most commonly associated with human infection, H. heilmanii and H. felis have also been isolated from humans, but at lower frequencies than H. pylori. Helicobacter infects over 50% of adult populations in developed countries and nearly 100% in developing countries and some Pacific rim countries, making it one of the most prevalent infections worldwide.

Helicobacter is routinely recovered from gastric biopsies of humans with histological evidence of gastritis and peptic ulceration. Indeed, H. pylori is now recognized as an important pathogen of humans, in that the chronic gastritis it causes is a risk factor for the development of peptic ulcer diseases and gastric carcinoma. It is thus highly desirable to develop safe and effective methods for preventing and treating Helicobacter infection.

SUMMARY OF THE INVENTION

The invention provides a method of inducing an immune response against Helicobacter in a mammal. This method involves mucosally (e.g., orally) administering to a mammal (e.g., a human) an attenuated Salmonella (e.g., S. typhi (e.g., CVD908-htrA or CVD908) or S. typhimurium (e.g., BRD509 or BRD807)) vector including a nucleic acid molecule encoding a Helicobacter antigen (e.g., a urease, a urease subunit, or an immunogenic fragment thereof), and parenterally administering to the mammal a Helicobacter antigen (e.g., a urease, a urease subunit, or an immunogenic fragment thereof), optionally, in association with an adjuvant, such as an aluminum compound (e.g., alum). The nucleic acid molecule encoding the Helicobacter antigen can be under the control of a promoter, such as an htrA or a nirB promoter. The antigen used in the mucosal administration can be different from, cross-reactive with, or, preferably, identical to the parenterally administered antigen. In a preferred embodiment, the mucosal administration primes an immune response to an antigen, and the parenteral administration boosts an immune response to the antigen. A mammal treated according to the method of the invention can be at risk of developing, but not have, a Helicobacter infection, or can have a Helicobacter infection. That is, the method can be used to prevent or to treat Helicobacter infection.

The invention also provides an attenuated Salmonella (e.g., S. typhi (e.g., CVD908-htrA or CVD908) or S. typhimurium (e.g., BRD509 or BRD807)) vector including a nucleic acid molecule encoding a Helicobacter antigen, e.g., a urease, a urease subunit, or an immunogenic fragment thereof, expressed as a fission protein that can be selectively targeted to the outer membrane or secreted from the cell. The nucleic acid molecule encoding the Helicobacter antigen can be under the control of a promoter, such as an htrA or a nirB promoter.

Other features and advantages of the invention will be apparent from the following detailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an expression plasmid pH/NUR3) used in Salmonella immunizations.

FIG. 2A is a graph showing the urease-specific serum antibody (IgG2a) response of mice that were mucosally primed with S. typhimurium-vectored urease, followed by parenteral boosting with urease and alum.

FIG. 2B is a graph showing the T helper phenotype (IgG1/IgG2a ratio) of mice that were mucosally primed with S. typhimurium-vectored urease, followed by parenteral boosting with urease and alum.

FIG. 3A is a graph showing protection against Helicobacter infection in mice that were mucosally primed with S. typhimurium-vectored urease, followed by parenteral boosting with urease and alum.

FIG. 3B is a table showing protection against Helicobacter infection in mice that were mucosally primed with S. typhimurium-vectored urease, followed by parenteral boosting with urease and alum, as log ₁₀ reduction in comparison to a no treatment control group.

FIG. 4 provides the nucleic acid sequence (SEQ ID NO:1) and amino acid sequence (SEQ ID NO:2) of plasmid pHUR3.

FIG. 5 is a schematic representation of some relevant features of pHUR3.

DETAILED DESCRIPTION

This invention provides an immunization method against Helicobacter infection that involves: (i) mucosal administration of an attenuated Salmonella vector containing a nucleic acid molecule encoding a Helicobacter antigen, and (ii) parenteral administration of a Helicobacter antigen, preferably, in association with an adjuvant. The method can be used to prevent or to treat Helicobacter infection in a mammal, such as a human. Also, the mucosal administration can be used to prime an immune response to an antigen, and the parenteral administration can be used to boost an immune response to the antigen. The invention also provides Salmonella vectors for use in this method. Salmonella vectors, Helicobacter antigens, and adjuvants that can be used in the method of the invention are first described, as follows. Then, details of the immunization method of the invention, and examples of its efficacy, are provided.

Salmonella Vectors

Numerous attenuated Salmonella vectors that can be used in the invention are known in the art, and can be derived from species such as, for example, S. typhi, S. typhimurium, S. enteritidis, S. dublin, S. Minnesota, and S. choleraesuis. The vectors can be attenuated chemically (e.g., Ty21a, Swiss Serums and Vaccines, Berna Products) or, preferably, by genetic mutagenesis (e.g., Ty800). For example, attenuation can be achieved by inactivation of key regulatory genes or genes necessary for in vivo survival. For example, the following genes can be inactivated: cya, crp, and asd (cAMP metabolism; see, e.g., Curtiss et al., Vaccine 6:155-160, 1988; Nakayama et al., BioTechnology 6:693, 1988; WO 92/11361), adenylate cyclase and the cAMP receptor (U.S. Pat. No. 5,389,368), cdt (invasion of liver and spleen), phoP/phoQ (two component regulator; see, e.g., Fields et al., Science 243:1059-1062, 1989; U.S. Pat. No. 5,424,065), ompR (control of capsule and porin expression; see, e.g., Dorman et al., Infection and Immunity 57:2136-2140, 1989), outer membrane proteins (U.S. Pat. No. 5,527,529), reverse mutants of streptomycin mutants (U.S. Pat. No. 4,350,684), genes in pathogenicity islands (Shea et al., Infection and Immunity 67:213-219, 1999; WO 99/37759), SPI-2 (invasion of Peyer's patches), Dam (DNA methylation), htrA (heat shock protein; U.S. Pat. No. 5,804,194), and other heat shock proteins (U.S. Pat. No. 5,804,194). The vectors can also be attenuated by auxotrophic mutations, such as mutations in any of the aroA, aroC, aroD (aromatic compounds), purA, or guaAB (purines) genes (see, e.g., U.S. Pat. No. 5,770,214).

Preferably, the mutations in the Salmonella strains used in the invention are non-reverting mutations, i.e., mutations that cannot be repaired in a single step. Mutations of this sort include deletions, inversions, insertions, and substitutions. Preferably, there is more than one mutation in the vector. Methods of making such mutations are well known in the art.

Specific examples of Salmonella vectors that can be used in the invention include S. typhi mutant strains, for example, CVD908 S. typhi Ty2 ΔaroC/ΔaroD (Hone et al., Vaccine 9:810-816, 1991), CVD908-htrA S. typhi Ty2 ΔaroC/ΔaroD/ΔhtrA (Tacket et al., Infection and Immunity 65:452-456, 1997), BRD1116 S. typhi Ty2 ΔaroA/ΔaroC/ΔhtrA (Lowe et al., Infection and Immunity 67:700-707, 1999), S. typhi ΔaroA/ΔaroE (U.S. Pat. No. 5,770,214; deposited at PHLS, NCTC, 61 Colindale Avenue, London NW9 5HT under Accession No. 25 NCTC 12164), S. typhi Ty2 ΔaroA/ΔaroC Km-R (U.S. Pat. No. 5,770,214; deposited at PHLS, NCTC, 61 Colindale Avenue, London NW9 5HT under Accession No. NCTC 12165), and S. typhi ΔaroA/ΔaroD (U.S. Pat. No. 5,770,214; deposited at PHLS, NCTC, 61 Colindale Avenue, London NW9 5HT under Accession No. NCTC 122309). It has been shown that one of these, CVD908-htrA, is safe and immunogenic in phase I (Tacket et al., Infection and Immunity 65:452-456, 1997) and phase II studies in a total of 100 adult volunteers.

Specific examples of S. typhimurium mutant strains that can be used in the invention include BRD509 S. typhimurium ΔaroA/ΔaroD (Strugnell et al., Infection and Immunity 60:3994-4002, 1992), BRD807 S. typhimurium ΔaroA/ΔhtrA (Chatfield et al., Microbial Pathogenesis 12:145-151, 1992; U.S. Pat. No. 5,804,194; deposited at PHLS, NCTC, 61 Colindale Avenue, London NW9 5HT under Accession No. NCTC 12459), BRD698 (U.S. Pat. No. 5,804,194; deposited at PHLS, NCTC, 61 Colindale Avenue, London NW9 5HT under Accession No. NCTC 12457), and BRD726 (U.S. Pat. No. 5,804,194; deposited at PHLS, NCTC, 61 Colindale Avenue, London NW9 5HT under Accession No. NCTC 12458).

Additional examples of Salmonella mutant strains that can be used in the invention are described in the following publications: double aro mutants (WO 89/05856, U.S. Pat. No. 5,770,214), htrA mutants (WO 91/15572, U.S. Pat. No. 5,804,194), and ompR mutants (U.S. Pat. No. 5,527,529). Also see, for example, Nakayama et al., BioTechnology 6:693, 1988 and WO 92/11361. In addition, there are numerous alternative strains of S. typhi and S. typhimurium described in the literature or known in the art that are also attenuated in their virulence, and have been shown to induce immune responses against heterologous antigens. Any of these strains can be used in the method of the present invention.

Any of the attenuated Salmonella strains described above, or others, can be used in the method of the invention to administer a Helicobacter antigen to a mammal for vaccination against Helicobacter infection. This can be accomplished by introducing into the attenuated Salmonella strain a nucleic molecule encoding a Helicobacter antigen. The antigen-encoding nucleic acid molecule to be introduced into the attenuated Salmonella strain can be present, for example, in a plasmid vector (e.g., pHUR3, pHUR4, pNUR3, or pNUR4 (see below)) that includes a regulatory sequence, such as a promoter, and, optionally, a sequence encoding a secretion signal (e.g., a bacterial hemolysin (hly) secretion signal; WO 87/06953, U.S. Pat. No. 5,143,830).

The promoter can be a prokaryotic promoter, for example, a Salmonella promoter, which directs expression of the Helicobacter antigen in the Salmonella vector. Examples of such promoters include the htrA promoter (WO 95/20665), the nirB promoter (WO 92/15689, U.S. Pat. No. 5,547,664), the ssaH promoter (Valdivia et al., Science 277:2007-2011, 1997), the ompR promoter, and any other Salmonella or other bacterial promoter that is upregulated when Salmonella is taken up by mammalian cells. Alternatively, the promoter can be a eukaryotic promoter, such as the cytomegalovirus promoter. Use of such promoters allows for expression of target antigen in a eukaryotic cell, with Salmonella acting as the delivery vehicle for this DNA immunization approach. The construction of such vectors is known in the art. Of course, numerous eukaryotic promoters are known in the art and can be used in the invention.

Introduction of a plasmid into an attenuated Salmonella strain can be accomplished using any of a number of standard methods, such as electroporation or bacteriophage transduction (Turner et al., Infection and Immunity 61:5374-5380, 1993). Also see, e.g., Ausubel et al., Current Protocols in Molecular Biology, John Wiley & Sons Inc., 1994, and Ward et al., Infection and Immunity 67(5):2145-2152, 1999, for methods of introducing plasmids into bacteria, such as Salmonella.

Helicobacter Antigens

Preferred antigens for use in the invention are Helicobacter (e.g., H. pylori or H. felis) proteins (i.e., peptides or polypeptides), other components Helicobacter (e.g., lipopolysaccharides, carbohydrates, or nucleic acid molecules), or immunogenic fragments thereof. Preferably, the same or a similar (e.g., a fragment) antigen is used in the mucosal administration step as in the parenteral administration step, however, the antigen used in each of these steps can differ. Also, preferably, the mucosally administered antigen primes an immune response to the antigen, and the parenterally administered antigen boosts an immune response to the same antigen. For the mucosal administration step, a nucleic acid molecule (e.g., a DNA molecule) encoding a desired antigen is inserted into an attenuated Salmonella vector, as is described above. For the parenteral administration step, the antigen can be, for example, purified from a bacterial culture or produced using standard recombinant or chemical synthetic methods. Methods for identifying immunogenic fragments of polypeptide antigens are known in the art, and can be employed in preparing antigens for use in the method of the invention (see, e.g., Sturniolo et al., Nature Biotechnology, "Generation of Tissue-Specific and Promiscuous HLA Ligand Databases Using DNA Microarrays and Virtual HLA Class II Matrices," June, 1999). Additional antigens that can be used in the parenteral administration step are whole Helicobacter bacteria and non-purified protein preparations, such as Helicobacter lysates.

The antigens used in the invention can be produced as fusion proteins, which are polypeptides containing amino acid sequences corresponding to two or more proteins (or fragments thereof) that are normally separate proteins, linked together by a peptide bond(s). Fusion proteins generally are synthesized by expression of a hybrid gene, containing nucleotides encoding each of the individual polypeptides that make up the fusion protein. An example of an antigenic fusion protein that can be used in the invention is one that contains a cholera toxin (CT) or an E. coli heat-labile toxin (LT) adjuvant (e.g., a toxin A or B subunit, or a fragment or derivative thereof having adjuvant activity) fused to an H. pylori antigen, e.g., a urease antigen. Another type of fusion protein included in the invention consists of an antigen fused to a polypeptide (e.g., glutathione S-transferase (GST)) that facilitates purification of the fusion protein. Still another type of fusion protein that can be used in the invention is a fusion with a polypeptide that targets the expressed protein to cells of the immune system. For example, fusions with CD4 or Staph A can be used. Proteins used as antigens in the invention can also be covalently coupled or chemically cross-linked to adjuvants, using standard methods.

The most preferred H. pylori antigens for use in the invention are urease antigens, which include, e.g., immunogenic fragments or subunits (e.g., UreA or UreB) of urease. Most preferred urease antigens are enzymatically inactive, recombinant multimeric urease complexes, produced as described in Lee et al., WO 96/33732. A number of other immunogenic H. pylori antigens can be administered according to the invention, e.g., catalase (WO 95/27506), HspA and HspB (WO 94/26901), lactoferrin receptor (WO 97/13784), p76 (WO 97/12908), p32 (WO 97/12909), BabA and BabB (WO 97/47646), AlpA (WO 96/41880), AlpB (WO 97/11182), as well as the antigens described in WO 96/38475, WO 96/40893, WO 97/19098, WO 97/37044, WO 98/18323, WO 97/37044, WO 97/4764, WO 98/04702, and WO 98/32768. Additional preferred antigens for use in the invention are GHPO 1516, GHPO 789, GHPO 386, GHPO 1615, GHPO 1360, GHPO 1320, GHPO 639, GHPO 792, GHPO 536, GHPO 525, GHPO 1275, GHPO 1688, GHPO 706, GHPO 419, GHPO 1595, GHPO 1398, GHPO 986, GHPO 1282, GHPO 1056, GHPO 1443, GHPO 13, GHPO 109, GHPO 257, GHPO 1034, GHPO 236, GHPO 1166, GHPO 1351, and GHPO 1420 (WO 98/21225, WO 98/43478, and WO 98/43479), as well as other antigens described in these publications.

Adjuvants

Although not required, the attenuated Salmonella vectors described above for mucosal administration step can be administered with a mucosal adjuvant. The adjuvant can be admixed with the Salmonella vector or expressed in the Salmonella vector (e.g., as a fusion protein with an antigen, see above), either from an integrated nucleic acid molecule or episomally, e.g., on a plasmid. Such adjuvants can be chosen from bacterial toxins, e.g., the cholera toxin (CT), the E. coli heat-labile toxin (LT), the Clostridium difficile toxin, and the Pertussis toxin (PT), or combinations, subunits, toxoids, fragments, homologs, derivatives, fusions, or mutants that are derived therefrom and have adjuvant activity. For example, it is possible to use a purified preparation of the native cholera toxin B subunit (CTB) or a polypeptide including the carboxyl-terminal repeats of C. difficile toxin A (WO 97/02836). Preferably, a mutant is used in which toxicity is reduced. Such mutants are described in, e.g., WO 95/17211 (mutant CT Arg-7-Lys), WO 96/6627 (mutant LT Arg-192-Gly), and WO 95/34323 (mutant PT Arg-9-Lys and Glu-129-Gly). Other LT mutants that can be used include at least one of the following mutations: Ser-63-Lys, Ala-69-Gly, Glu-110-Asp, and Glu-112-Asp. Other compounds, such as MPLA, PLGA, and QS-21, can also be used as adjuvants for the mucosal route.

Adjuvants for use in parenteral administration include, for example, aluminum compounds (e.g., alum), such as aluminum hydroxide, aluminum phosphate, and aluminum hydroxy phosphate. The antigen can be precipitated with, or adsorbed onto, the aluminum compound using standard methods.

In addition to aluminum compounds, a large number of appropriate adjuvants for administration by the systemic or parenteral route exist in the art and can be used in the invention. For example, liposomes; ISCOMS; microspheres; protein chochleates; vesicles consisting of nonionic surfactants; cationic amphiphilic dispersions in water; oil/water emulsions; muramidyldipeptide (MDP) and its derivatives, such as glucosyl muramidyldipeptide (GMDP), threonyl-MDP, murametide, and murapalmitin; QuilA and its subfractions; as well as various other compounds, such as DC-chol; monophosphoryl-lipid A (MPLA) major lipopolysaccharide from the wall of a bacterium, for example, E. coli, S. minnesota, S. typhimurium, Shigella flexneri, or N. meningitidus; algan-glucan; gamma-inulin; calcitriol; and loxoribine can be used. Other adjuvants, such as RIBI (ImmunoChem, Hamilton, MT) and polyphosphazene (WO 95/2415), can also be used in parenteral administration.

Useful liposomes for the purposes of the present invention can be selected, for example, from pH-sensitive liposomes, such as those formed by mixing cholesterol hemisuccinate (CHEMS) and dioleyl phosphatidyl ethanolamine (DOPE); liposomes containing cationic lipids recognized for their fusiogenic properties, such as 3-beta-(N-(N',N'-dimethylamino-ethane)carbamoyl)cholesterol (DC-chol) and its equivalents, which are described in U.S. Pat. No. 5,283,185 and WO 96/14831; dimethyldioctadecylammonium bromide (DDAB) and the BAY compounds described in EP 91645 and EP 206 037, for example, Bay R1005 (N-(2-deoxy-2-L-leucylamino-beta-D-glucopyranosyl)-N-octa-decyldodecanoylamide acetate; and liposomes containing MTP-PE, a lipophilic derivative of MDP (muramidyldipeptide). These liposomes are useful as adjuvants with all of the antigens described herein.

Useful ISCOMs for the purposes of the present invention can be selected, for example, from those compounds of QuilA or of QS-21 combined with cholesterol and, optionally, also with a phospholipid, such as phosphatidylcholine. These are particularly advantageous for the formulation of the lipid-containing antigens.

Useful microspheres for the purposes of the present invention can be formed, for example, from compounds such as polylactide-co-glycolide (PLAGA), alginate, chitosan, polyphosphazene, and numerous other polymers.

Useful protein chochleates for the purposes of the present invention can be selected, for example, from those formed from cholesterol and, optionally, an additional phospholipid, such as phosphatidylcholine. These are especially advantageous for the formulation of the lipid-containing antigens.

Useful vesicles consisting of nonionic surfactants for the purposes of the present invention can be, for example, formed by a mixture of 1-mono-palmitoyl glycerol, cholesterol, and dicetylphosphate. They are an alternative to conventional liposomes, and can be used for the formulation of all of the antigens described herein.

Useful oil/water emulsions for the purposes of the present invention can be selected, for example, from MF59 (Biocine-Chiron), SAF1 (Syntex), and the montanides ISA51 and ISA720 (Seppic).

A useful adjuvant for the purposes of the present invention can also be a fraction derived from the bark of the South American tree Quillaja Saponaria Molina, for example, QS-21, a fraction purified by HPLC chromatography as is described in U.S. Pat. No. 5,057,540. Since some toxicity may be associated with QS-21, it may be advantageous to use it in liposomes based on sterol, as is described in WO 96/33739.

Induction of an Immune Response Against Helicobacter

The method of the invention can be used to prevent Helicobacter infection in a patient, as well as to treat an ongoing Helicobacter infection in a patient. Thus, gastroduodenal diseases associated with these infections, including acute, chronic, or atrophic gastritis, and peptic ulcers, e.g., gastric or duodenal ulcers, can be prevented or treated using the method of the invention.

As is noted above, the method of the invention involves mucosal (e.g., oral, intranasal, intragastric, pulmonary, intestinal, rectal, ocular, vaginal, or urinary tract) administration of a Salmonella vector including a nucleic acid molecule that encodes a Helicobacter antigen, followed by parenteral (e.g., intramuscular, subcutaneous, intradermal, intraepidermal, intravenous, or intraperitoneal) administration of a Helicobacter antigen, preferably in association with an adjuvant. The antigen used in the mucosal prime can be different from, cross-reactive with, or, preferably, identical to the parenterally administered antigen. Preferably, the mucosal administration step primes an immune response to an antigen, and the parenteral administration step boosts an immune response to the antigen. Also included in the invention are vaccination methods involving parenteral priming and mucosal boosting (e.g., with a Salmonella vector including a nucleic acid molecule encoding a Helicobacter antigen), and parenteral administration of a Salmonella vector including a nucleic acid molecule encoding a Helicobacter antigen.

Attenuated Salmonella vectors, antigens, formulations, adjuvants, administration regimens, specific mucosal and parenteral routes, and dosages to be used in the method of the invention can readily be determined by one skilled in the art. For example, 5×10⁶-5×10¹⁰ colony forming units, e.g., 5×10⁸ colony forming units, of an attenuated Salmonella vector can be used in the mucosal administration, and 5-1000 μg, e.g., 100 μg, antigen, can be used in the parenteral administration. The mucosal administration can take place only once or two or more (e.g., three, four, or five) times, for example, separated by two, three, or four days or weeks. Similarly, the parenteral administration can take place once or two or more (e.g., three, four, or five) times, separated by weeks, months, or years from each other or the mucosal administration.

In one example of an immunization regimen that can be used, a patient is primed with two doses of an attenuated Salmonella vector (e.g., S. typhi CVD908-htrA or CVD908, or S. typhimurium BRD509 or BRD807) expressing an antigen (e.g., urease from plasmid pHUR3, pHUR4, pNUR3, or pNUR4) on days 0 and 21, and then parenterally boosted on day 51 or later with an antigen (e.g., urease) and an adjuvant (e.g., alum). The details of construction of pHUR3 and pNUR3, which each include an ampicillin resistance gene, are described below. pHUR4 and pNUR4 are constructed by removing the ampicillin resistance gene from pHUR3 and pNUR3, respectively, by digestion with the restriction endonuclease RcaI, and cloning into the digested vectors a kanamycin resistance gene that can be obtained from plasmid pUC4K (Pharmacia) by digestion with EcoRI.

A useful pharmaceutical composition for the purposes of the present invention can be manufactured in a conventional manner. In particular, it can be formulated with a pharmaceutically acceptable carrier or diluent, e.g., water or a saline solution. In general, the diluent or carrier can be selected according to the mode and route of administration and according to standard pharmaceutical practices. Appropriate carriers or diluents, as well as what is essential for the preparation of a pharmaceutical composition, are described, e.g., in Remington's Pharmaceutical Sciences (18^th edition), ed. A. Gennaro, 1990, Mack Publishing Company, Easton, Pa., a standard reference book in this field. As a specific example, the attenuated Salmonella vectors of the invention can be formulated in a tablet for oral administration (see, e.g., U.S. Pat. No. 5,804,194).

The therapeutic or prophylactic efficacy of the method of the invention can be evaluated according to standard methods, e.g., by measuring the induction of an immune response or the induction of therapeutic or protective immunity using, e.g., the mouse/H. felis model and the procedures described in Lee et al., Eur. J. Gastroenterology and Hepatology 7:303, 1995 or Lee et al., J. Infect. Dis. 172:161, 1995. Persons skilled in this art will realize that H. felis can be replaced in the mouse model by another Helicobacter species. For example, the efficacy of the method is, preferably, evaluated in a mouse model using an H. pylori strain adapted to mice. The efficacy can be determined by comparing the level of infection in gastric tissue (e.g., by measuring the urease activity, bacterial load, or condition of the gastritis) with that in a control group. A therapeutic effect or a protective effect exists when infection is reduced compared with a control group. Experimental methods and results showing the efficacy of the present method is described as follows.

Experimental Methods and Results

Construction of ureAB expression plasmids under the control of the nirB and htrA promoters--Method 1

A ureAB expression plasmid is constructed by subcloning a PCR product containing the ureAB genes (amplified from plasmid pORV273) into plasmid vector ptetnir15. Plasmid pORV273 is obtained from OraVax, Inc., Cambridge, Mass. Plasmid ptetnir15 has been described (Chatfield et al., Bio/Technology 10:888-892, 1992; Oxer et al., Nucl. Acids Res. 19:1889-1892, 1991). This vector was modified by standard techniques known in the art, to introduce into the vector a suitable restriction site for subcloning other genes for optimal expression under control of the nirB promoter. An NcoI site was introduced 10 basepairs 3' to the Shine-Dalgarno sequence of ptetnir15, and the resultant plasmid is designated ptetnir15/mod. Plasmid ptetnir15/mod, carried in strain BRD940, is obtained from Peptide Therapeutics Ltd., Cambridge, U.K.

The ureAB gene is amplified by PCR from pORV273 using Turbo Pfu polymerase (Stratagene), which has 3'-5' proof-reading activity, and two primers, designated orafor and orarev. Primer orafor introduces EcoRI and BspHI sites immediately upstream of the initiating codon of the ureA gene. Primer orarev binds approximately 18 basepairs downstream of the BamHI site that is located 45 basepairs downstream of the termination codon of the ureB gene.

The PCR reaction includes 0.1 μg pORV273 and 100 pmol each of primers orafor (5'-TAG GGA ATT CTC ATG AAA CTC ACC CCA AAA G-3' (SEQ ID NO:3)) and orarev (5'-GCC AAC TTA GCT TCC TTT CGG G-3' (SEQ ID NO:4)) per 100 μl reaction and utilizes 25 cycles, with an annealing temperature of 50°C C. The resulting 2.4 kb PCR product is purified from a 1% agarose gel using a Qiaquick gel extraction kit (Qiagen). As is described below, the actual method used in the generation of pNUR and pHUR differed from this description in the sequence of orarev. Therefore, the method described here may need to be adapted in ways known to those skilled in the art by changing, for example, the precise annealing temperature or the number of cycles required to give sufficient product, or even in the sequence of the primer orarev.

The PCR product is digested with BspHI+BamHI, and purified with a Promega Wizard DNA clean-up kit. Plasmid ptetnir15/mod is digested with NcoI+BamHI (the NcoI site is 10 basepairs 3' to the Shine-Dalgarno sequence of ptetnir15, and generates a cohesive end that is compatible with BspHI), and dephosphorylated using shrimp alkaline phosphatase. The largest fragment from the digestion of ptetnir 15/mod is isolated from a 1% agarose gel using a Qiaquick gel extraction kit (Qiagen), and ligated to the digested PCR product using the Ligator Express Kit (Clontech). Ligations are transformed into electrocompetent E. coli TG1cells (Stratagene).

Plasmids from ampicillin-resistant transformants are screened for the presence of the full length, 2.4 kb ureAB gene by restriction analysis. The ureAB gene from plasmid pORV273 has a BamHI site within the coding sequence. However, in a small number of ptetnir 15/mod+ureAB transformants, incomplete digestion or re-ligation of the two ureAB fragments yields the full length ureAB PCR product. The orientation of the ureAB gene in the ptetnir15-derived plasmid is confirmed by PCR, and a plasmid with the full length ureAB gene, in the correct orientation is designated pNUR.

The nirB promoter in plasmid pNUR is replaced with the htrA promoter from phtrAcore, which is obtained from Peptide Therapeutics Ltd., Cambridge, U.K. Plasmids pNUR and phtrAcore are digested with PstI and Bg/II. Digested pNUR is dephosphorylated with shrimp alkaline phosphatase. The digestion products are run on a 1% agarose gel, and a 0.8 kb fragment containing the htrA promoter from the phtrAcore digestion and the 4.0 kb fragment from pNUR lacking the nirB promoter are extracted from the gel using a Qiagen Qiaquick gel extraction kit. The two fragments are ligated together (Clontech Ligator express kit), and transformed into electrocompetent E. coli TG1 cells (Stratagene). Transformants are screened for the presence of the htrA promoter by PCR using primer pairs specific for htrA (5902/5904) or nirB (5901/5904). A plasmid with the htrA promoter and a full length ureAB gene is designated pHUR.

The nucleotide sequence across the promoter region and ureAB genes of final plasmids are confirmed. Samples of the plasmids are prepared using the Qiagen "Plasmid midi kit" (Catalog No. 12143), and the DNA sequence determined by standard techniques. Oligonucleotides 5901 to 5919 (see below) can be used, and allow nucleotide sequence determination of both DNA strands. Oligonucleotides 5901 and 5902 hybridize within nirB and htrA, respectively, while 5919 hybridizes within ptetnir15/mod, downstream of the ureAB genes. The other oligonucleotides hybridize within the ureAB genes. The data confirm that the nucleotide sequence across the recombinant region of all plasmids are as expected.

Plasmids pNUR and pHUR are introduced into S. typhimurium strains such as, e.g., BRD509 and BRD807, and S. typhi strains such as, e.g., CVD908 and BRD948, by electroporation and selection of ampicillin-resistant colonies.

Construction of ureAB Expression Plasmids Under the Control of the nirB and htrA Promoters--Method 2

The protocol described above is one example of many by which one skilled in the art can derive an expression plasmid suitable for directing the synthesis of an H. pylori antigen, e.g., urease, under the control of the htrA or nirB promoter in an attenuated strain of Salmonella. Alternative primers can be used in the PCR amplification of the genes from the starting plasmid, and alternative strategies for the introduction of the gene via alternative restriction sites are possible. One such alternative was employed in the construction of plasmids pNUR3 and pHUR3. During the design of the primers for PCR, a sequence error in the database-deposited gene sequence caused the 3' end of the ureB gene to be incorrectly identified. A primer was synthesized for the PCR amplification that, in fact, resulted in a non-native sequence of the gene, containing an additional 49 codons after the genuine termination codon. This error was subsequently corrected by the method described below, yielding a final plasmid with a sequence identical to that of the plasmid that would be produced by the strategy described above. This method is described in further detail, as follows.

As is described above, plasmid pORV273 was obtained from OraVax Inc. Plasmid ptetnir 15 has been described (Chatfield et al., Bio/Technology 10:888-892, 1992; Oxer et al., Nucl. Acids Res. 19:1889-1892, 1991), and this vector was modified by standard techniques, to introduce into the vector a suitable restriction site for subcloning other genes for optimal expression under control of the nirB promoter. An NcoI site was introduced 10 basepairs 3' to the Shine-Dalgarno sequence of ptetnir15, and the resultant plasmid was designated ptetnir 15/mod. Plasmid ptetnir15/mod, carried in strain BRD940, was obtained from the culture collection of Peptide Therapeutics Ltd., Cambridge, U.K.

The ureAB gene was amplified by PCR from pORV273 using Turbo Pfu polymerase (Stratagene), which has 3'-5' proof-reading activity and two primers, designated orafor and orarev. Primer orafor introduces EcoRi and BspHI sites immediately upstream of the initiating codon of the ureA gene. Primer orarev introduces a BamHI and a PstI site just before the correct 3' end of the ureAB gene. Subsequent digestion and cloning, as is described below, resulted in the deletion of the correct termination codon of ureB, with the result that transcription continued into the vector sequence until an in-frame stop codon was reached, adding 49 amino acids to the translated protein.

The PCR reaction included 0.1 μg pORV273 and 100 pmol each of primers orafor (5'-TAG GGA ATT CTC ATG AAA CTC ACC CCA AAA G-3' (SEQ ID NO:3)) and orarev (5'-TCT ACT GCA GGA TCC AAA ATG CTA AAG AGT TGC G-3' (SEQ ID NO:5)) per 100 μl reaction, and utilized 25 cycles, with an annealing temperature of 50°C C. The resulting 2.4 kb PCR product was purified from a 1% agarose gel using a Qiaquick gel extraction kit (Qiagen). The PCR product was digested with BspHI+BamHI, and purified with a Promega Wizard DNA clean-up kit. Plasmid ptetnir15/mod was digested with NcoI+BamHI (the NcoI site is 10 basepairs 3' to the Shine-Dalgarno sequence of ptetnir15, and generates a cohesive end that is compatible with BspHI), and dephosphorylated using shrimp alkaline phosphatase. The largest fragment from the digestion of ptetnir 15/mod was isolated from a 1% agarose gel using a Qiaquick gel extraction kit (Qiagen), and ligated to the digested PCR product using the Ligator Express Kit (Clontech). Ligations were transformed into electrocompetent E. coli TG1 cells (Stratagene).

Plasmids from ampicillin-resistant transformants were screened for the presence of the full length, 2.4 kb ureAB gene by restriction analysis. The ureAB gene from plasmid pORV273 has a BamHI site within the coding sequence. However, in a small number of ptetnir15/mod+ureAB transform ants, incomplete digestion or re-ligation of the two ureAB fragments yielded the full length ureAB PCR product. The orientation of the ureAB gene in the ptetnir15-derived plasmid was confirmed by PCR and a plasmid with the full length ureAB gene, in the correct orientation was designated pNUR1.

The nirB promoter in plasmid pNUR1 was replaced with the htrA promoter from phtrAcore, which is obtained from Peptide Therapeutics Ltd., Cambridge, U.K. Plasmids pNUR1 and phtrAcore were digested with PstI and BglII. Digested pNUR1 was dephosphorylated with shrimp alkaline phosphatase. The digests were run on a 1% agarose gel, and a 0.8 kb fragment containing the htrA promoter from the phtrAcore digest and the 4.0 kb fragment from pNUR1 lacking the nirB promoter were extracted from the gel using a Qiagen Qiaquick gel extraction kit. The two fragments were ligated together (Clontech Ligator express kit) and transformed into electrocompetent E. coli TG1 cells (Stratagene). Transformants were screened for the presence of the htrA promoter by PCR using primer pairs specific for htrA (5902/5904) or nirB (5901/5904). A plasmid with the htrA promoter and a full length ureAB gene was designated pHUR1.

Subsequent to this it was discovered that there had been a cloning error in the 3' terminal portion of ureB, resulting in a translated product with an additional 49 amino acids from both pHUR1 and pNUR1. This was corrected by replacing the small BamHI fragment containing the C-terminus of the ureB gene with the corresponding, and correct, fragment from pORV272. pORV273, pHUR1, and pNUR1 were digested with BamHI, and the small fragment from the pORV273 digestion was ligated to the large fragment from the pHUR1 and pNUR1 digestions. Clones were screened for orientation of the insert, and clones with the correct orientation were designated pHUR3 and pNUR3. These clones were characterized by full nucleotide sequencing of the region including the promoter and the complete ureAB gene on both strands, and found to be correct.

The nucleotide sequences across the nirB promoter and ureAB genes of pNUR1 and of the htrA promoter region of pHUR1 were confirmed. Samples of the two plasmids were prepared using the Qiagen "Plasmid midi kit" (Catalogue No. 12143), and the DNA sequence was determined by standard techniques known in the art. Oligonucleotides 5901 to 5919 were used, which allow nucleotide sequence determination of both DNA strands. Oligonucleotides 5901 and 5902 hybridize within nirB and htrA, respectively, while 5919 hybridizes within ptetnir 15/mod downstream of the ureAB genes. The other oligonucleotides hybridize within the ureAB genes. These were diluted to 1 pmol μl^-1, packed in dry ice with the plasmid samples, and sent to Cambridge Bioscience (Cambridge) for nucleotide sequence determination. The data confirmed that the nucleotide sequence across the recombinant region of all three plasmids was as expected.

Sequences of primers that can be used in the invention, as is described above, are as follows.

5901

Primes within nirB promoter ∼60 basepairs upstream of SD sequence

TCA AAT GGT ACC CCT TGC TGA (SEQ ID NO:6)

5902

Primes within htrA promoter ∼60 basepairs upstream of SD sequence

TAT TCC GGA ACT TCG CGT TA (SEQ ID NO:7)

5903

Primes ∼250 basepairs downstream from start of urea gene

TGT TTC CTG ATG GGA CTA AAC TC (SEQ ID NO:8)

5904

Reverse primes ∼300 basepairs downstream from start of urea gene

ACC AGG AAC TAA TTT ACC ATT G (SEQ ID NO:9)

5905

Primes ∼550 basepairs downstream from start of urea gene

TTG ATT GAC ATT GGC GGT AAC (SEQ ID NO:10)

5906

Reverse primes ∼600 basepairs from start of urea gene

GTT GTC TGC TTG TCT ATC AAC C (SEQ ID NO:11)

5907

Primes ∼150 basepairs downstream from start of ureB gene

GGT GGC GGT AAA ACC CTA AGA G (SEQ ID NO:12)

5908

Reverse primes ∼180 basepairs downstream of ureB gene

CTT TGC TAG GGT TGT TAG ATT G (SEQ ID NO:13)

5909

Primes ∼400 basepairs downstream from start of ureB gene

AAT CCC TAC AGC TTT TGC AAG C (SEQ ID NO:14)

5910

Reverse primes ∼500 basepairs from start of ureB gene

GTG CCA TCA GCA GGA CCG GTT C (SEQ ID NO:15)

5911

Primes ∼750 basepairs from start of ureB gene

ATC GCC ACA GAC ACT TTG AAT G (SEQ ID NO:16)

5912

Reverse primes ∼820 basepairs downstream from start of ureB gene

TAG CAG CCA TAG TGT CTT CTA C (SEQ ID NO:17)

5913

Primes ∼1050 basepairs downstream from start of ureB gene

TGA AGA CAC TTT GCA TGA CAT G (SEQ ID NO:18)

5914

Reverse primes 1080 basepairs downstream of ureB gene

TGA GAG TCA GAA CTG GTG ATT G (SEQ ID NO:19)

5915

Primes ∼1350 basepairs downstream from start of ureB gene

CAT GAT CAT CAA AGG CGG ATT C (SEQ ID NO:20)

5916

Reverse primes ∼1380 basepairs downstream from start of ureB

GAA GCG TTC GCA TCG CCC ATT TG (SEQ ID NO:21)

5917

Primes ∼1650 basepairs from start of ureB

TCG TGG ATG GCA AAG AAG TAA C (SEQ ID NO:22)

5918

Reverse primes ∼1680 basepairs from start of ureB

GCG CCA AGC TCA CTT TAT TG (SEQ ID NO:23)

5919

Reverse primes 80 basepairs downstream of BamHI site downstream of ureB

CAA CGA CAG GAG CAC GAT CAT G (SEQ ID NO:24)

The nucleotide sequences across the promoter regions and ureAB genes of the final plasmids, pHUR3 and pNUR3, were also confirmed. E. coli MC1061 cells containing the plasmids were sent to Cambridge Biosciences Ltd., who prepared plasmid DNA and determined the nucleotide sequences of the promoter and ureAB genes of both plasmids. The data confirmed that the nucleotide sequence across the relevant region of both plasmids was as expected. The sequence of plasmid pHUR3 is shown in FIG. 4, and a plasmid map showing its relevant features is provided in FIG. 5.

Plasmids pNUR and pHUR were introduced into S. typhimurium strains BRD509 and BRD807, and S. typhi strains CVD908 and BRD948, by electroporation and selection of ampicillin-resistant colonies.

Immunization and Protection Experiments

Inbred Balb/C mice were immunized by the intragastric route with live, attenuated Salmonella typhimurium (1E10 CFU/ml) expressing urease apoenzyme on day 0 (FIG. 1). Animals were boosted twice on days 21 and 35 with 10 μg soluble, recombinant urease plus aluminum hydroxide (200 μg) by the parenteral route. Fourteen days later, serum antibody responses to urease were measured. Controls included: (1) prime-boost with the Salmonella parental control strains (BRD509 ΔaroA/ΔaroD (Strugnell et al., Infection and Immunity 60:3994-4002, 1992) and BRD807ΔaroA/ΔhtrA (Chatfield et al., Microbial Pathogenesis 12:145-151, 1992)) minus the urease construct, (2) mucosal priming with LT in place of Salmonella (gold standard), and (3) parenteral immunization with urease plus alum alone. Attenuated S. typhimurium (ΔaroA/ΔaroD) expressing urease under the transcriptional control of either an htrA promoter (pHUR3) or the nirB promoter (pNUR3) induced an elevated IgG2a response against urease that was greater than the gold standard using LT-Alum (FIG. 2A). A comparable response to LT-Alum was induced with S. typhimurium (ΔaroA/ΔhtrA) carrying the same urease constructs (FIG. 2A). Analysis of the IgG1/IgG2a ratio demonstrated the induction of a Th1 response with the double aro mutant, and a more balanced response with the Δaro/ΔhtrA mutant strain (FIG. 2B). Urease-specific antibody in FIG. 2A is expressed as EU/ml on a logarithmic scale and median response is indicated by the bar.

The level of protective efficacy employing S. typhimurium-vectored urease in a prime-boost strategy was determined. FIG. 3A shows the results of quantitative H. pylori culture of mice immunized on day 0 with 1E10 CFU/ml live attenuated S. typhimurium (ΔaroA/ΔaroD or ΔaroA/ΔhtrA) and boosted on days 21 and 35 with urease (10 μg) plus alum (200 μg). Three weeks later, animals were challenged with H. pylori (1E7 CFU/ml) and efficacy was assessed in gastric tissue 4 weeks later using quantitative culture. Strains including the urease constructs are indicated in the key of FIG. 3A. FIG. 3B shows protection depicted as log₁₀ reduction in comparison to the no treatment (Tx) control group. A significant reduction in bacterial burden was observed when attenuated Salmonella expressing urease was administered as part of a prime-boost regimen with alum (Wilcoxon rank sum compared to parental control strain). No significant difference was observed between group 1 (pHUR3-Alum) and group 7 (LT-Alum).

All patents and publications cited above are hereby incorporated by reference in their entirety.

Claims

1. A method of inducing an immune response against helicobacter in a mammal, said method comprising the steps of:

mucosally administering to said mammal an attenuated salmonella vector comprising a nucleic acid molecule encoding a helicobacter antigen, and

parenterally administering to said mammal a helicobacter antigen.

2. The method of claim 1, wherein said attenuated salmonella vector is administered orally to said mammal.

3. The method of claim 1, wherein said helicobacter antigen is a urease, a urease subunit, or an immunogenic fragment thereof.

4. The method of claim 1, wherein said mammal is at risk of developing, but does not have, a helicobacter infection.

5. The method of claim 1, wherein said mammal has a helicobacter infection.

6. The method of claim 1, wherein said parenteral administration of said helicobacter antigen further includes parenteral administration of an adjuvant.

7. The method of claim 6, wherein said adjuvant is an aluminum compound.

8. The method of claim 7, wherein said aluminum compound is alum.

9. The method of claim 1, wherein said attenuated salmonella vector is a salmonella typhi vector.

10. The method of claim 9, wherein said salmonella typhi vector is CVD908-htrA or CVD908.

11. The method of claim 1, wherein the attenuated salmonella vector is a salmonella typhimurium vector.

12. The method of claim 11, wherein said salmonella typhimurium vector is BRD509 or BRD807.

13. The method of claim 1, wherein said attenuated salmonella vector further comprises an htrA promoter.

14. The method of claim 1, wherein said attenuated salmonella vector further comprises a nirB promoter.

15. The method of claim 1, wherein said mucosal administration primes an immune response to an antigen and said parenteral administration boosts an immune response to said antigen.